Apparatus for coagulation of colloidal dispersions



APPARATUS FOR COAGULATION OF COLLOIDAL DISPERSIONS Filed Nov. 2, 1959 IN V EN TOR. perm/Is E prayer United States Patent 3,179,380 APPARATUS FOR COAGULATION 0F COLLOIDAL DISPERSIONS Dennis E. Drayer, Frankfort, S. Dak., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Nov. 2, 1959, Ser. No. 850,394 5 Claims. (Cl. 259-8) This invention relates to an apparatus for the coagulation of colloidal dispersions. It more particularly relates to an apparatus for the continuous coagulation of synthetic latices and like colloidal dispersions.

It is conventional practice to prepare various synthetic resins by polymerizing an aqueous dispersion of monomeric material in the presence of a micelle-forming surface active agent, thereby preparing a relatively stable colloidal dispersion of the synthetic resinous material in water. Such a dispersion is usually referred to as a synthetic latex.

Such a process is frequently referred to as the emulsion polymerization technique. It is frequently employed to obtain polymers and copolymers having particularly desirable properties which are not easily and economically prepared by other polymerization methods.

conventionally, such resins have been separated from the liquid medium by the addition of electrolytes to the colloidal dispersion. This results in coagulation of the resin from the dispersion. Frequently, it is desirable to coagulate this type of dispersion in such a manner that the product is separated as a granular material that contains only a relatively small portion of water. In contrast, some coagulating techniques may result merely in the formation of a paste-like mass. Frequently, this problem is solved by diluting the latex to a solids content in the rangeof about 5 to about 25 weight percent, based on the total weight of the dispersion.

Usually suitable electrolyte solutions employed as coagulants contain polyvalent anions, although monovalent anions may frequently be employed. The dispersion is agitated and the temperature is raised until the formation of granular material has been obtained. When agitation ceases, the granular material settles and the aqueous phase is substantially free of resinous material. frequently serves to give a more solid and processable granule or crumb.

The heating.

The resulting slurry is allowed to settle and the supernatant liquid decanted. The solids are reslurried in fresh portions of water to remove excess electrolyte and other water-soluble contaminants which may be present, such lysts. After the required number of washing cycles have been performed, the product is again slurried, filtered, and dried.

t The crumb or granule prepared by such a process -as surface active. agents and residual salts from the catashould have sufiicientmechanical strength to withstand,

filtration and shipping. The granules should havesufficient mechanical strength so that attrition will not take place during processing or shipping.

Coagulation by the batch technique generally requires large equipment occupying a large area. Also, a batch type of surface active agent employed during the polymerization, and the distribution of the surface active agent between the water phase and the surface of the latex particle afterv the polymerization is complete. Consequently,

.70 appreciable variations in the latex coagulation characteristics may occur between batches of the finished latex,

3,179,380 Patented Apr. 20, 1965 despite the fact that the resin recovered from various latex batches may appear to have substantially identical physical properties, such as molecular weight and the like.

Variations in basic latex coagulation characteristics can give rise to serious difliculties in batch coagulation operations. These variations often require that a series of pilot or experimental coagulation runs be made prior to the coagulation of a freshly prepared batch of latex. Only through long experiences in correlating pilot or other experimental or developmental runs with large scale runs made with the same latex can a reasonable prediction of large scale conditions be made. Such a procedure leaves an undesirable area of uncertainity and may frequently incur excessive expense and additional labor.

It is. well-known practice to coagulate synthetic latices into sheets, and to express the entrapped liquid from the coagulant by means of pressure rolls or similar apparatus. The resultant sheet is ground, washed, and dried. A procedure of this type is relatively costly and disadvantagcously yields an undesirable type of crumb having a very high internal surface which usually occludes a large quantity of the polymerization medium within the crumb.

It is desirable that as much as possible of the coagulant and the polymerization medium be removed prior to the drying in order that the resultant resin may have the maxi- .mum light and heat stability.

It would be advantageous if there were available an apparatus for the coagulation of synthetic latices and like colloidal dispersions which were simple and would prepare a desired granule or crumb. I

It would also be beneficial if such a method would permit the apparatus to be capable of rapid adjustment to compensate for variations in the starting materials.

Further, it would be advantageous if such an apparatus were capable of coagulating a synthetic latex or like colloidaldispersion with a minimum exposure of the desired product to higher temperatures.

' It would be most beneficial if such an apparatus were capable of providing a product which has a relatively uniform'and readily controllable crumb size.

'It would also be most advantageous if such an apparatus would provide a crumb having good mechanical stability and high resistance to dusting and attrition.

These advantages and other benefits may be obtained .by providing a generally cylindrical and substantially vertically disposed coagulating vessel having a length to diameter ratio of at least 8:1; the generally cylindrical walls of said vessel having therein a discharge port positioned near the top of said vessel, one inlet port near the bottom of said vessel, and at least three inlet ports disposed in spaced vertical relationship between said bottom and said top ports; with said apparatus having an agitator in said vessel extending vertically downward into the vessel a distance of at least-about percent of the length of said vessel. i

A colloidal dispersion may be coagulated according to the apparatus of the invention by providing ahelically flowing stream of coagulant, introducing into said stream of coagulant a stream of latex, introducing into the latexcoagulant streamt a heated diluent for said latex; and subsequently introducing a cold liquid diluent for said later; into saidhot diluted-latex-coagulant stream.

,Further features. and advantages of the invention will become apparent from the following description and specification, taken in conjunction with the accompanying drawing, wherein the; sole figure is a schematic representation of a cross-sectional view of a coagulating vessel constructed in accordance with the invention.

There is shown in the drawing a coagulating apparatus ,orcoagulator which is indicated generally by the reference number .10." The,coagulator 10 comprises a'coagulating vessel lZ having a length to diameter ratio of at least 8: 1. At the upper end of the vessel 12 there is positioned a discharge port. 14. At the lower or bottom end of the vessel 12 is a coagulant inlet or port 16. Intermediate between the ports 14 and 16 is a latex inlet or port 18, a hot water inlet or port 20, and a cold water inlet or port 22.

Rotatably supported within the vessel is an agitator which is indicated generally by the reference number 30. The agitator is made up of the shaft 31 and turbine type impellers 37, 33, 39, and 40 aiiixed thereon. Also affixed to the shaft 31 and rotating therewith are forwarding or pumping impellers 41 and 42. The agitator 30 is supported at the top by a bearing 32 and at the bottom by a bearing 34. The shaft 31 is rotated by means of the variable speed drive means 33. Positioned within the generally cylindrical wall of the coagulating vessel 12 are thermocouples 44, 45, and 46. The latex inlet port 18 is a coaxial inlet comprising a latex supply conduit 48 and annular water supply port 49.

In accordance with the operation of the present inven- 7 tion, a coagulant solution is introduced through the port 16. Water near the temperature of the latex is introduced through annular supply ported. Hot water is fed into port 20. Cold water is introduced into the vessel'in the upper section through port 22. The flow rates of the coagulant and water into the latex port 18 and the hot adjusted to result in suitable temperatures within the coagulator. Such an operation is facilitated by the thermocouples 44, 45, and 46. In their absence, however, calculation based on flow rate and temperature of the various streams will readily result in a reasonable close approximation of the desired temperature.

Rotation of the agitator 30 is then initiated. The latex to be coagulated is introduced through the latex conduit 48; The resulting product slurry is delivered from the discharge port 14 and thereafter processed by conventional means.

The inventory time of the polymer in the coagulato-r is generally desired to be on the order of one-half to ten minutes, depending on the particular latex which is employed. In general, latices which may be coagulated by batch techniques may be coagulated by practice of the present invention. In this connection, latices to which the method and apparatus of the invention may be em- ,ployed with particular advantage are described in United States Letters Patents Numbers 2,538,025 and 2,640,050. In general, the crumb size may be increased by decreasing the speed of agitation or decreased by increasing the speed of agitation. It isusually advantageous to employ a variable speed drive in conjunction withthe agitator creased appreciably above the softening point of the resin being coagulated, there will be a tendency for very large particles to be formed. Some change in particle size may also be obtained by altering the design and size of the impeller employed in the vicinity of port 18.

' Generally, more violent agitation in the lower section iof the' vessel adjacent to port '18 willresult in reduced article size. Although the agitation is further increased, endency will be noted, for the coagulant particle s still further increased,.the polymer will: tend to mulate on the walls of the agitator in this area. mil "build-up of polymer will resultif' the coagulant be'pressed together to form larger. crumbs. If agita- 4 temperature is too hot or the concentration of the coagulant is too low. For a given type of latex, such temperatures and conditions may be determined by small scale batch laboratory coagulation and the optimum coagulating conditions obtained by minor adjustments or flow rates, agitation, and temperatures in the continuous coagulating apparatus of the present invention.

When employing latices prepared in accordance with United States Letters Patents Numbers 2,640,050 and 2,538,025, it is usually desirable to provide the forwarding or pumping impellers 41 and 42 in substantially the positions illustrated. However, when employing latices containing resins having densities that more closely approach that of the water, the pumping impellers 41 and 42 may be omitted. If the length todiameter of the coagulating vessel is in a ratio that is appreciably higher than 8: 1, respectively, the rate of flow is frequently sufficient to overcome the settling effect of the higher density polymer in the coagulating medium. In such cases the forwarding impellers are not necessary.

Various configurations of the impellers may be employed. No particular shape or design is found to be and cold water to ports 20 and 22, respectively, are

quire a slight alteration of temperature or a flow rate. In general, the impellers should have a clearance from the inner walls of the vessel 12 that is in excess of about two particle diameters of the coagulated product being prepared. However, closer clearances may be employed, if desired.

In the drawing, port 16 has been illustrated as pro- .viding a stream of coagulant flowing substantially and 'ploy an apparatus that is relatively corrosion resistant.

' the5port 20 of the coagulant fed to the port 16 is inr polymer and subsequent processing equipment.

solution to reduce the undesirable chemical effects of the coagulant. Other streams may also be introduced to the coagulator." For example, in a case where aluminum sulfate is employed as coagulant, it may be advantageous to add potassium or sodium hydroxide to neutralize. the acidic eflect of the coagulant on both the A port maybe provided between ports 20 and 22 to facilitate such an addition.

A coagulator' in accordance with the invention was constructed from type 304 stainless steel. The coagulating vessel 12 was fabricated from a 48 inch-length of 3 inch Schedule 40' pipe, capped on each end with reducers carrying the agitator bearings 32 and '34. The upper reducer was provided with a 1 /2 inch :outlet 14, "Posi- -tioned along the wall" of the vessel 12 were ports 18, '20, and 22, each of /2 inch pipe.

The thermocouples 44, 45, and 46 were enclosed in a inch stainless steel tubing, brazed in a 4 inch inch pipe plug, and inserted into a'mating opening the vessel 12 wall. The agitator rotatedby' a direct, connected, variable speed motor 010- erating at a rate between about 200 and 400 revolutions per minute.

Comparative coagulations were run on similar batches of latices prepared according to United States Letters Patent 2,538,025 employing both conventional batch techniques and coagulations in accordance with the present invention. A much more uniform and desirable crumb particle size distribution was obtained when employing the apparatus of the invention than was obtained in a batch coagulation.

Coagulation rates of about 200 pounds per hour (based on dry solids) were obtained when employing latex having a solids content of about 30 percent. The heat stability of the polymer was also improved and the inorganic residues reduced as indicated by light transmission measurements made on solutions of the resultant polymers.

Many of a wide variety of latices have been successfully coagulated by the apparatus of the present invention. Some examples are copolymers of vinyl chloride and vinylidene chloride, varying in composition from about percent vinyl chloride to about 80 percent vinyl chloride; vinylidene chloride/acrylonitrile copolymers vary in composition from about 10 percent acrylonitrile to about 30 percent acrylonitrile; and copolymers of vinylidene chloride with various acrylates, as well as similar copolymers latices.

As is apparent, the apparatus is susceptible of being embodied with various alterations and modifications from that which has been described in the preceding de scription and specification. For this reason it is to be fully understood that all of the foregoing is merely intended to be illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention excepting as it is set forth and defined in the hereto appended claims.

What is claimed is:

1. A generally cylindrical and substantially vertically disposed vessel having a length to diameter ratio of at least about 8:1, the vessel having an internally smooth generally cylindrical wall, the generally cylindrical wall of the vessel defining a discharge port near the top, an inlet port near the bottom and at least three inlet ports disposed in spaced vertical relationship between the bottom and top ports, the inlet port adjacent the bottom inlet port being in communication with a latex inlet conduit surrounded by an annular inlet, an agitator extending vertically downwardly into the vessel for a distance vf at least about percent of the length of the vessel, the agitator having at least one impeller, the impeller being spaced from the inner wall of the vessel.

2. The apparatus of claim 1, wherein the agitator extends substantially the entire length of the vessel.

3. The apparatus of claim 1, and including, in addition thereto and in combination therewith, at least one forwarding impeller on said agitator.

4. The apparatus of claim 1, and including, in addition thereto and in combination therewith, a means for varying the rotational speed of the agitator.

5. The apparatus of claim 1, and including, in addition thereto and in combination therewith, a lower agitator bearing, said bearing being liquid lubricated.

References Cited by the Examiner UNITED STATES PATENTS 1,629,200 5/27 Buhtz.

2,577,095 12/51 Walker 259-8 X 2,628,077 2/ 53 Handwerk 2599 X 2,673,193 3/54 Kolvoort 260-928 2,706,108 4/55 Miner 2598 2,717,248 9/55 Vaughn et a1. 26092.8 2,746,729 5/56 Eakins 259--8 CHARLES A. WILLMUTH, Primary Examiner.

H. BUSTEIN, Examiner. 

1. A GENERALLY CYLINDRICAL AND SUBSTANTIALLY VERTICALLY DISPOSED VESSEL HAVING A LENGTH TO DIAMETER RATIO OF AT LEAST ABOUT 8:1, THE VESSEL HAVING AN INTERNALLY SMOOTH GENERALLY CYLINDRICAL WALL, THE GENERALLY CYLINDRICAL WALL OF THE VESSEL DEFINING A DISCHARGE PORT NEAR THE TOP, AN INLET PORT NEAR THE BOTTOM AND AT LEAST THREE INLET PORTS DISPOSED IN SPACED VERTICAL RELATIONSHIP BETWEEN THE BOTTOM AND TOP PORTS, THE INLET PORT ADJACENT THE BOTTOM INLET PORT BEING IN COMMUNICATION WITH A LATEX INLET CONDUIT SURROUNDED BY AN ANNULAR INLET, AN AGITATOR EXTENDING VERTICALLY DOWNWARDLY INTO THE VESSEL FOR A DISTANCE OF AT LEAST ABOUT 80 PERCENT OF THE LENGTH OF THE VESSEL, THE 